This invention relates to a torque converter lockup clutch control apparatus for use with an automotive vehicle having a multi-cylinder type internal combustion engine.
Torque converter lockup clutch control apparatus have been proposed, for example, in Japanese Patent Kokai Nos. 57-163732, 59-89861 and 61-136057, to reduce undesirable sounds sympathetic with vibrations excited by engine output torque fluctuation. The engine output torque fluctuation includes two components. The first component is induced by successive complete combustions in the engine and it excites a high degree of force which vibrates the vehicle at a frequency ranging from about 50 Hz to about 58 Hz. This vibration frequency, which corresponds to the time interval between the successive combustions in the engine, tends to cause a sympathetic sound. The second component is induced with incomplete combustion taking place in one or more engine cylinders and it excites a low degree of force which vibrates the vehicle at a frequency ranging from about 10 Hz to about 18 Hz. This vibration frequency, which corresponds to the time intervals at which incomplete combustion takes place, tends to cause a judder.
Although the conventional lockup clutch control apparatus are sufficient to reduce the sympathetic sound caused by the first component of the engine torque fluctuation induced when the engine is operating with complete combustion taking place in all of the engine cylinders, they cannot reduce the judder and sympathetic sound caused by the second component of the engine torque fluctuation induced when the engine is operating with incomplete combustion taking place in one or more engine cylinders.